74 



FOREST PRODUCTS 



The liquor is then filtered and evaporated to the desired density or con- 

 centration. Multiple evaporators are used for this purpose and about 

 1400 gal. of water are evaporated for every cord of wood leached in open 

 extractors. In a plant producing 250 bbl. of extract daily about 225,000 

 gal. of water must be evaporated. In the evaporation process the mini- 

 mum temperature of the steam is said to be 220^" F. The temperature 

 in the other steps is still lower. Finally the concentrated liquor is 

 pumped into a series of settling tanks. After settling and cooling, the 

 concentrated liquor is placed into tank cars for shipment. 



P?iotooraph &y U. S. Forest Service. 



Fig. 15. — A large leather tannery at Andrews, North Carolina. Two years' supply of bark 

 piled ready for use on the left. Hemlock bark has been the mainstay for tanning leathers 

 until the advent, in recent years, of foreign materials such as quebracho, myrobalan 

 nuts, sumach, valonia, mangrove bark, etc. 



The yield of 25 per cent tannin extract secured from a cord of chest- 

 nut wood containing i6o cu. ft. is from 700 to 900 lb. The cost of chest- 

 nut wood delivered at the plant varies from about $4.50 to $5.00 per 

 cord of 160 cu. ft. before the war. The average price secured for extract 

 of about 25 per cent strength was about $4.06 per unit of tannin in 1914. 

 Consequently, the yield was from $8.00 to $9.50 per cord with a pro- 

 ducing charge of about $7.50 to $8.00 per cord, the balance being interest 

 and profit. 



The factories making chestnut extract are exceedingly complicated 

 and specialized industries and considerable capital for investment is 



